After completing his PhD, Stark held appointments as a research sociologist at the Survey Research Center and at the Center for the Study of Law and Society. After teaching as Professor of Sociology and of Comparative Religion at the University of Washington for 32 years, Stark moved to Baylor University in 2004, where he is co-director of the Institute for Studies of Religion.[2] He is an advocate of the application of the rational choice theory in the sociology of religion, which he calls the theory of religious economy.[3]

During the late 1970s and 1980s, Stark worked with William Sims Bainbridge on the Stark–Bainbridge theory of religion,[3] and co-wrote the books The Future of Religion (1985) and A Theory of Religion (1987) with Bainbridge. Nowadays their theory, which aims to explain religious involvement in terms of rewards and compensators, is seen as a precursor of the more explicit recourse to economic principles in the study of religion as later developed by Laurence Iannaccone and others.[5][6]

Stark has proposed in The Rise of Christianity that Christianity grew through gradual individual conversions via social networks of family, friends and colleagues. His main contribution, by comparing documented evidence of Christianity's spread in the Roman Empire with the history of the LDS church in the 19th and 20th centuries, was to illustrate that a sustained and continuous growth could lead to huge growth within 200 years. This use of exponential growth as a driver to explain the growth of the church without the need for mass conversions (deemed necessary by historians until then) is now widely accepted.

Stark has suggested that Christianity grew because it treated women better than pagan religions. He also suggested that making Christianity the state religion of the Roman Empire weakened the faithfulness of the Christian community by bringing in people who did not really believe or had a weaker belief. This is consistent with Stark's published observations of contemporary religious movements, where once-successful faith movements gradually decline in fervor due to the free rider problem.

In 2004 The American Enterprise, an online publication of the American Enterprise Institute, published an article by Stark, "Facts, Fable and Darwin," critical of the stifling of debate on evolution. Stark criticized the "Darwinian Crusade" and their "tactic of claiming that the only choice is between Darwin and Bible literalism." Though not a creationist himself, he believes that though "the theory of evolution is regarded as the invincible challenge to all religious claims, it is taken for granted among the leading biological scientists that the origin of species has yet to be explained." He suggests that governments "lift the requirement that high school texts enshrine Darwin's failed attempt as an eternal truth."[7]

In their 1987 book A Theory of Religion, Stark and Bainbridge describe themselves as "personally incapable of religious faith".[8] While reluctant to discuss his own religious views, he stated in a 2004 interview that he was not a man of faith, but also not an atheist.[9] In a 2007 interview, after accepting an appointment at Baylor University, Stark indicated that his self-understanding had changed and that he could now be described as an "independent Christian." In this interview Stark recollects that he has "always been a “cultural” Christian" understood by him as having "been strongly committed to Western Civilization." Of his previous positions he wrote: "I was never an atheist, but I probably could have been best described as an agnostic."[10]

The Churching of America 1776-1992: Winners and Losers in Our Religious Economy (1992), with Roger Finke; 2nd edition under name The Churching of America 1776-2005: Winners and Losers in Our Religious Economy (2005)

John Lofland and Rodney Stark. Becoming a World-Saver: A Theory of Conversion to a Deviant Perspective American Sociological Review of 1965. (an early and influential conversion theory based on field work among Unification Church members)[11]